The problem of presenting a readily changeable alphanumeric readout in a small space has been solved in many different fashions, as exemplified by neon-glow-discharge tubes, liquid crystal readouts, solid-state electroluminescent devices, and the like. Most such arrangements require operating signals which themselves contain most or all of the information to be displayed, and in any case are in general poorly adapted to large scale readouts, such as may be seen readily from a considerable distance. Further, a general problem with light-emitting displays is illegibility when the ambient light level is high. Opaque displays, in contrast, increase in visibility as the ambient light increases.
A need exists for a mechanically sound, readily and quickly changeable and accurate display for such diversified uses as destination indicators for buses, advertising signs, indicators of ambient temperature, time of day, and the like.